A known spintronics device, to which two properties (charge and spin) of electrons are applied, is a magnetoresistive random access memory (hereafter, referred to as MRAM), which is nonvolatile and allows rewriting of data (e.g., see Non-Patent Literature 1).
Such an MRAM stores data by means of the tunnel magnetoresistance effect (hereafter, abbreviated as TMR effect) of a magnetic tunnel junction element (hereafter, abbreviated as MTJ element) that has a three-layered structure in which, for example, a very thin tunnel barrier (insulator layer) is sandwiched between ferromagnetic layers, forming a magnetic tunnel junction (hereafter, referred to as MTJ). One of the two ferromagnetic layers is a fixed magnetization layer (pinned layer) having a fixed magnetization direction, and the other is a free magnetization layer (free layer) having a reversible magnetization direction. In a typical MTJ element, data “0” and “1” are associated with an antiparallel state where the fixed magnetization layer and the free magnetization layer have the opposite magnetization directions and a parallel state where they have the same magnetization direction, and data is stored as “0” or “1” defined by the magnetization direction of the free magnetization layer.
In writing data into the MTJ element, the magnetization direction of the free magnetization layer is reversed depending on the data. Several techniques are used for reversing the magnetization direction. For example, a magnetic field application technique, a spin-transfer torque technique (spin injection technique), and the like are known. In the magnetic field application technique, a given magnetic field is applied to a free magnetization layer to reverse the magnetization direction of the free magnetization layer. Meanwhile, in the spin-transfer torque technique, an electron is injected to a free magnetization layer to exert a torque on the magnetic moment of the free magnetization layer, which reverses the magnetization direction of the free magnetization layer to a desired direction. For data reading, a voltage is applied across the MTJ element to create an electric current flow through the MTJ element, and resistance of the MTJ element is sensed by using the electric current. The magnetization direction of the free magnetization layer is identified from the magnitude of the resistance so as to determine whether the data is “1” or “0”.